sx05 nc8 ch11bnew.fm 4 protists page thursday, june...

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Section

4

Protists

Objectives

After completing the lesson, students will be able to

A.11.1.1

Describe the characteristics of animal-like protists and give examples.

A.11.1.2

Describe the characteristics of plantlike protists and give examples.

A.11.1.3

Describe the characteristics of funguslike protists and give examples.

Target Reading Skill

Outlining

Explain that using an outline format helps organize information by main topic, subtopic, and details.

Answers

ProtistsI. What is a Protist?

II. Animal-Like ProtistsA. Protozoans With PseudopodsB. Protozoans With CiliaC. Protozoans With FlagellaD. Protozoans That Are Parasites

III. Plantlike ProtistsA. DiatomsB. DinoflagellatesC. EuglenoidsD. Red AlgaeE. Green AlgaeF. Brown Algae

IV. Funguslike ProtistsA. Slime MoldsB. Water Molds C. Downy Mildews

Teaching Resources

•

Transparency A18

Preteach

Build Background Knowledge

Characterizing Living Organisms

Review characteristics of living things. Before class, place several drops of vegetable oil in a small dish of water. Add a few drops of green food coloring to the water. Place the dish on an overhead projector. Ask students:

How can you tell whether the blobs you see are alive?

(Sample answer: Check for reaction to stimuli, taking in food, breathing, and movement.)

L2

Skills Focus

Observing

Materials

plastic dropper, pond water, microscope slide, cover slip, microscope

Time

25 minutes

Tips

Have students predict what they might observe in the water. Suggest students use their high-power objective lenses if they have them.

L1

Expected Outcome

Both algae and protozoans should be visible. Green algae have a greenish tint, but most organisms appear colorless. Organisms with flagella or pseudopods could be either protozoans or algae.

Think It Over

Students will probably associate movement with life.

468 ◆

4 Protists

Reading PreviewKey Concept• What are the characteristics of

animal-like, plantlike, and funguslike protists?

Key Terms• protist • protozoan • pseudopod• contractile vacuole • cilia • symbiosis • mutualism • algae • pigment • spore

Target Reading SkillOutlining As you read, make an outline about protists that you can use for review. Use the red section headings for the main topics and the blue headings for the subtopics.

Look at the objects in Figure 19. What do they look like to you?Jewels? Beads? Stained glass ornaments? You might be sur-prised to learn that these beautiful, delicate structures are thewalls of unicellular organisms called diatoms. Diatoms live inboth fresh water and salt water and are an important foodsource for many marine organisms. They have been called the“jewels of the sea.”

FIGURE 19Diatoms These glasslike organisms are classified as protists.

I. What is a protist?

II. Animal-like protists

A. Protozoans with pseudopods

B.

C.

Protists

What Lives in a Drop of Pond Water?1. Use a plastic dropper to place a drop of pond

water on a microscope slide.2. Put the slide under your microscope’s low-

power lens. Focus on the objects you see.3. Find at least three different objects that

you think might be organisms. Observe them for a few minutes.

4. Draw the three organisms in your notebook. Below each sketch, describe the movements or behaviors of the organism. Wash your hands thoroughly when you have finished.

Think It OverObserving What characteristics did you observe that made you think that each organism was alive?

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Differentiated Instruction

Instruct

What Is a Protist?

Teach Key Concepts

Describing Protist Characteristics

Focus

Emphasize that protists are highly diverse but do share some traits.

Teach

Ask:

Which traits are shared by all protists?

(They are eukaryotes that live in moist environments.)

Name the diverse protist categories.

(Animal-like, plantlike, funguslike)

Apply

Ask:

What characteristic would a plantlike protist have?

(The ability to make its own food)

learning modality: verbal

Independent PracticeTeaching Resources

•

Guided Reading and Study Worksheet:

Protists

Student Edition on Audio CD

Animal-Like Protists

Teach Key Concepts

Comparing Protists and Animals

Focus

Ask:

What are some animal traits?

(Sample answers: They are consumers; most can move about to obtain food.)

.

Teach

Explain that animal-like protists are heterotrophs and that most can move about to obtain food. Ask:

What name is given to animal-like protists?

(Protozoans)

How do protozoans differ from animals?

(Protozoans are unicellular; animals are multicellular.)

Apply

Ask:

What characteristic can be used to classify protozoans?

(How they move)


L2

L2

English Learners/Beginning

Comprehension: Modified Cloze

Distribute a simple paragraph about protists, leaving some strategic words blank. For example, “Animal-like protists are called _____. They can be grouped by how they _____ and _____.” Provide students a list of the correct answers, and have them fill in each blank with one of those words.


L1L1

English Learners/Intermediate

Comprehension: Modified Cloze

Distribute the cloze paragraph designed for Beginning Level, but add some incorrect answers to the list of correct answers. Students can work in pairs to correct each other’s answers, and to collaborate in writing a definition, in English, of the words that they filled in.


L2

Monitor Progress L2

Answers

Figure 2

Structure, unicellular or multicellular; habitat

Moist environment

Chapter 11 ◆ 469

What Is a Protist?Diatoms are only one of the vast varieties of protists. Protists areeukaryotes that cannot be classified as animals, plants, or fungi.Because protists are so different from one another, you can thinkof them as the “odds and ends” kingdom. However, protists doshare some characteristics. In addition to being eukaryotes, allprotists live in moist surroundings.

The word that best describes protists is diversity. For exam-ple, most protists are unicellular, but some are multicellular.Some are heterotrophs, some are autotrophs, and others areboth. Some protists cannot move, while others zoom aroundtheir moist surroundings.

Because of the great variety of protists, scientists have pro-posed several ways of grouping these organisms. One useful wayof grouping protists is to divide them into three categories, basedon characteristics they share with organisms in other kingdoms:animal-like protists, plantlike protists, and funguslike protists.

In what kind of environment do all protists live?

Animal-Like ProtistsWhat image pops into your head when you think of an animal?A tiger chasing its prey? A snake slithering onto a rock? Mostpeople immediately associate animals with movement. In fact,movement is often involved with an important characteristicof animals—obtaining food. All animals are heterotrophs thatmust obtain food by eating other organisms.

Like animals, animal-like protists are heterotrophs, andmost are able to move from place to place to obtain food. Butunlike animals, animal-like protists, or protozoans (proh tuhZOH unz), are unicellular. Protozoans can be classified into fourgroups, based on the way they move and live.

FIGURE 20

ProtistsProtists include animal-like, plantlike, and funguslike organisms.Comparing and Contrasting In what ways do protists differ from one another?

These shells are the remains of unicellular, animal-like protists called foraminifera.

This red alga is a multicellular, plantlike protist found on ocean floors.

The yellow slime mold oozing off the leaf is a funguslike protist.

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Help Students Read

Previewing Visuals

Refer to the Content Refresher, which provides guidelines for Previewing Visuals. Before students read the section on protozoans with pseudopods and protozoans with cilia, have them study Figures 3 and 4 and read the labels. Call on student volunteers to name protozoan structures used for locomotion

(Cilia, pseudopods)

, feeding

(Food vacuole, oral groove)

, and reproduction

(Nucleus)

. Have students read the text in this section, then together discuss the functions of the structures observed prior to reading.

Observing Pseudopod Movement

Materials

plastic dropper, amoeba culture, microscope slide, cover slip, microscope

Time

20 minutes

Focus

Review with students the function of an amoeba’s pseudopods.

Teach

Have students place a drop of the amoeba culture on a slide, carefully add a cover slip, and then observe the organisms under low and high power.

Apply

Ask:

Can you tell when the amoeba is using its pseudopods to eat and when it is using them to move?

(Students may say that when the amoeba is eating, it wraps two pseudopods around the food; when it is moving, it puts out a pseudopod and flows into it.)

Students can sketch what they observe and label the parts of the amoeba. Observations should include the organism’s shape, size, and motion.

learning modality: visual

For:

Amoeba and Paramecium activity

Visit:

PHSchool.com

Web Code:

cep-1031

Students learn about two types of protozoans, the amoeba and the paramecium.

L1

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Protozoans With Pseudopods The amoeba in Figure 21belongs to the group of protozoans called sarcodines. Sarco-dines move and feed by forming pseudopods (SOO duhpahdz)—temporary bulges of the cell. The word pseudopodmeans “false foot.” Pseudopods form when cytoplasm flowstoward one location and the rest of the organism follows.Pseudopods enable sarcodines to move. For example, amoebasuse pseudopods to move away from bright light. Sarcodinesalso use pseudopods to trap food. The organism extends apseudopod on each side of the food particle. The two pseudo-pods then join together, trapping the particle inside.

Protozoans that live in fresh water, such as amoebas, have aproblem. Small particles, like those of water, pass easilythrough the cell membrane into the cytoplasm. If excess waterwere to build up inside the cell, the amoeba would burst. For-tunately, amoebas have a contractile vacuole (kun TRAK tilVAK yoo ohl), a structure that collects the extra water and thenexpels it from the cell.

For: Amoeba and Paramecium activityVisit: PHSchool.comWeb Code: cep-1031

FIGURE 21

Amoeba Amoebas are sarcodines that live in either water or soil. They feed on bacteria and smaller protists.

PseudopodAn amoeba uses pseudopods to move and feed. Pseudopods form when cytoplasm flows toward one location and the rest of the amoeba follows.

Contractile VacuoleThe contractile vacuole collects excess water from the cytoplasm and expels it from the cell.

Food VacuoleWhen the ends of two pseudopods fuse, they form a food vacuole. Food is broken down inside the food vacuole in the cytoplasm.

Cell MembraneBecause the cell membrane is very thin and flexible, an amoeba‘s shape changes constantly.

Cytoplasm

NucleusThe nucleus controls the cell’s functions and is involved in reproduction. Amoebas usually reproduce by binary fission.


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Use Visuals: Figures 3 and 4

Amoeba and Paramecium

Focus

Have students observe the figures.

Teach

Ask:

What do these two protists have in common?

(They eat the same things, and they both have nuclei, cytoplasm, food vacuoles, and contractile vacuoles.)

Ask:

What is different about them?

(Amoebas live in soil and water, paramecia only in water; paramecia move with cilia, amoebas move with pseudopods; paramecia ingest food into an oral groove, amoebas surround food with pseudopods; amoebas have one nucleus, paramecia have two.)

Apply

Ask:

What characteristics make the amoeba suited to life in either soil or water?

(Sample answer: It can change its shape and flow easily through different substances. The contractile vacuole allows excess water to be expelled.)

What characteristics make the paramecium suited to living only in water?

(Sample answer: Its two contractile vacuoles remove excess water from the cell. Their cilia, which move the paramecium through water and sweep food into the oral groove, may not be as effective in a solid environment such as soil. Their rigid shape may hinder movement through compact soil.)


Teaching Resources

•

Transparencies A19, A20

L1

Gifted and Talented

Investigating Protozoan Groups

Provide books or online sources on ciliate and sarcodine (amoeba) protozoans. Have students prepare and present a visual display that highlights the features of one of the two groups: the variety of protozoans in the group, what they eat, whether any cause disease to humans, and so forth.


L3

Less Proficient Readers

Identifying Protozoan Structures

Provide students with a list of amoeba and paramecium structures presented in Figures 3 and 4, and an accompanying list of their descriptions. Have students match structures with descriptions as they observe Figures 3 and 4 or the relevant transparencies.


L1

Monitor Progress L2

Oral Presentation

Have students compare and contrast the characteristics of an amoeba and a paramecium.

Answers

Hairlike projections from cells that move with a wavelike motion

Chapter 11 ◆ 471

Anal PoreWastes leave through the anal pore.

Oral GrooveThe oral groove is a funnel-like indentation lined with cilia. The cilia move water containing food into the vacuole that forms at the end of the oral groove.

CiliaThousands of cilia project through the pellicle. The beating cilia enable a paramecium to move smoothly in one direction.

Contractile VacuolesTwo contractile vacuoles collect excess water from the cytoplasm and expel it from the cell.

PellicleA stiff but flexible covering, called the pellicle, surrounds a paramecium and gives it shape.

Food VacuoleA food vacuole forms and pinches off from the oral groove. It moves into the cytoplasm. Inside the vacuole, the food is broken down and then distributed.

Large Nucleus

Cytoplasm

Small Nucleus

FIGURE 22

Paramecium Paramecia are ciliates that live mostly in fresh water. Like amoebas, paramecia feed on bacteria and smaller protists.

Protozoans With Cilia The second group of animal-likeprotists are the ciliates. Ciliates have structures called cilia (SIL

ee uh), which are hairlike projections from cells that move witha wavelike motion. Ciliates use their cilia to move and obtainfood. Cilia act something like tiny oars to move a ciliate. Theirmovement sweeps food into the organism.

The cells of ciliates, like the paramecium in Figure 22, arecomplex. Notice that the paramecium has two contractile vac-uoles that expel water from the cell. It also has more than onenucleus. The large nucleus controls the everyday tasks of thecell. The small nucleus functions in reproduction.

Paramecia usually reproduce asexually by binary fission.Sometimes, however, paramecia reproduce by conjugation.This occurs when two paramecia join together and exchangesome of their genetic material.

What are cilia?

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Modeling Animal-Like Protists

Materials

clay, paint, string, pipe cleaners, cardboard, and other materials of students’ choice

Time

30 minutes

Focus

Challenge small groups to design models of one of the four kinds of animal-like protists.

Teach

Have students consult photos in the text or in reference materials. Models should include unique details for each organism, with labels. Have students compare and contrast the models, explaining similarities and differences. They should note the structures, shapes, and methods of movement of the various animal-like protozoans.

Apply

Challenge groups to use their models to demonstrate how these organisms move or feed.

learning modality: kinesthetic

Integrating Health

Avoiding Health Threats of Parasites in Water

Ask students to describe ways that hikers can avoid ingesting

Giardia. (Sample answers: Carry enough water, use water purifying treatments, boil water before using.)

Inform students that the safest way to purify water of organisms is to boil it for at least three minutes. This will kill the organisms, but it will not necessarily make the water safe if the water also contains chemical pollutants.


L2

L1

472 ◆

FIGURE 23Giardia When people drink from freshwater streams and lakes, they can get hiker’s disease. Giardia intestinalis (inset) is the protozoan responsible for this disease. Inferring Why is it important for hikers to filter stream water?

FIGURE 24Malaria Mosquito Anopheles mosquitoes can carry the parasitic protozoan Plasmodium, which causes malaria in people.

Protozoans With Flagella The third group of protozoansare flagellates (FLAJ uh lits), protists that use long, whiplike fla-gella to move. A flagellate may have one or more flagella.

Some of these protozoans live inside the bodies of otherorganisms. For example, one type of flagellate lives in the intes-tines of termites. There, they digest the wood that the termiteseat, producing sugars for themselves and for the termites. Inturn, the termites protect the protozoans. The interactionbetween these two species is an example of symbiosis (sim beeOH sis)—a close relationship in which at least one of the spe-cies benefits. When both partners benefit from living together,the relationship is a type of symbiosis called mutualism.

Sometimes, however, a protozoan harms its host. Forexample, Giardia is a parasite in humans. Wild animals, such asbeavers, deposit Giardia in freshwater streams, rivers, and lakes.When a person drinks water containing Giardia, these protozo-ans attach to the person’s intestine, where they feed and repro-duce. The person develops a serious intestinal conditioncommonly called hiker’s disease.

Protozoans That Are Parasites The fourth type of proto-zoans are characterized more by the way they live than by theway they move. They are all parasites that feed on the cells andbody fluids of their hosts. These protozoans move in a varietyof ways. Some have flagella, and some depend on hosts fortransport. One even produces a layer of slime that allows it toslide from place to place!

Many of these parasites have more than one host. For exam-ple, Plasmodium is a protozoan that causes malaria, a disease ofthe blood. Two hosts are involved in Plasmodium’s life cycle—humans and a species of mosquitoes found in tropical areas.The disease spreads when a healthy mosquito bites a personwith malaria, becomes infected, and then bites a healthy person.Symptoms of malaria include high fevers that alternate withsevere chills. These symptoms can last for weeks, then disap-pear, only to reappear a few months later.

What is symbiosis?


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Plantlike Protists

Teach Key Concepts

Describing Plantlike Protists

Focus

Have students look at the pictures in this section of plantlike protists.

Teach

Ask:

What is the name commonly used for plantlike protists?

(Algae)

How are algae similar to plants?

(They are autotrophs—they can make their own food.)

What traits of algae vary greatly?

(Size—unicellular to colonies of thousands of cells; colors—green, red, brown, yellow, orange, or black)

Apply

Explain that algae can make their own food. Ask:

What important role do algae, like plants, play in the environment?

(They produce oxygen and serve as an important food source for other organisms.)

learning modality: logical/mathematical

Teaching Resources

•

Transparencies A21, A22

L2

Skills Focus

Inferring

Materials

paramecium culture,

Chlorella

culture, plastic dropper, microscope and slide, cotton fibers

Time

15 minutes

Tip

Students can also slow down the paramecia by placing a coverslip over the drop of culture and absorbing water from

L2

the edge of the coverslip with lens paper, or by adding a drop of 2–3% clear gelatin solution to the drop of culture.

Expected Outcome

Green food vacuoles form inside the paramecia as they ingest the

Chlorella

. Students should conclude that paramecia are heterotrophs, while

Chlorella

are autotrophs.


Monitor Progress L2

Oral Presentation

Ask students to give the other names for animal-like protists and plantlike protists.

(Animal-like—protozoans; plantlike—algae)

Answers

Figure 5

To remove disease-causing

Giardia

and other harmful organisms from the water

A close relationship between two species in which at least one of the species benefits

Chapter 11 ◆ 473

Flagella

Watching ProtistsIn this activity you will watch the interaction between paramecium, an animal-like protist, and Chlorella, a plantlike protist.

1. Use a plastic dropper to place 1 drop of

paramecium culture on a microscope slide. Add some cotton fibers to slow down the paramecia.

2. Use the microscope’s low-power objective to find some paramecia.

3. Add 1 drop of Chlorella to the paramecium culture on your slide.

4. Switch to high power and locate a paramecium. Observe what happens. Then wash your hands.

Inferring What evidence do you have that paramecia are heterotrophs? That Chlorella are autotrophs?

FIGURE 25Dinoflagellates Dinoflagellates whirl through the water with their flagella.

Plantlike ProtistsPlantlike protists, which are commonly called algae (AL jee),are extremely diverse. Like plants, algae are autotrophs. Mostare able to use the sun’s energy to make their own food.

Algae play a significant role in many environments. Forexample, algae that live near the surface of ponds, lakes, andoceans are an important food source for other organisms inthe water. In addition, much of the oxygen in Earth’s atmo-sphere is made by these algae.

Algae vary greatly in size. Some algae are unicellular, whileothers are multicellular. Still others are groups of unicellularorganisms that live together in colonies. Colonies can containfrom a few cells up to thousands of cells. In a colony, most cellscarry out all functions. But, some cells may become specializedto perform certain functions, such as reproduction.

Algae exist in a wide variety of colors because they containmany types of pigments—chemicals that produce color.Depending on their pigments, algae can be green, yellow, red,brown, orange, or even black.

Diatoms Diatoms are unicellular protists with beautifulglasslike cell walls. Some float near the surface of lakes oroceans. Others attach to objects such as rocks in shallow water.Diatoms are a food source for heterotrophs in the water. Manydiatoms can move by oozing chemicals out of slits in their cellwalls. They then glide in the slime.

When diatoms die, their cell walls collect on the bottoms ofoceans and lakes. Over time, they form layers of a coarse sub-stance called diatomaceous (dy uh tuh MAY shus) earth. Diato-maceous earth makes a good polishing agent and is used inhousehold scouring products. It is even used as an insecticide—the diatoms’ sharp cell walls puncture the bodies of insects.

Dinoflagellates Dinoflagellates (dy noh FLAJ uh lits) areunicellular algae surrounded by stiff plates that look like a suitof armor. Because they have different amounts of green,orange, and other pigments, dinoflagellates exist in a varietyof colors.

All dinoflagellates have two flagella held in groovesbetween their plates. When the flagella beat, thedinoflagellates twirl like toy tops as they movethrough the water. Many glow in the dark. Theylight up the ocean’s surface when disturbed by apassing boat or swimmer.


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Building Models of Algae

Materials

none

Time

15 minutes

Focus

Direct students to make a “living” model of how algae of various sizes take in food and eliminate waste.

Teach

Divide the class into three groups: unicellular algae, multicellular algae, and a colony of algae. Have each student act out the role of an individual algae cell. Give each group a deck of cards to use as a food source, and encourage the “cells” to act out how each organism accomplishes food intake and waste elimination.

Apply

Have students describe food intake and waste elimination in terms of whether they are individual or cooperative processes.

(Sample answers: unicellular: individual students pick up and put down cards without interacting; multicellular: cooperative model—one student picks up a card and passes it on, another puts it down; colony: both individual and cooperative.

learning modality: kinesthetic

Help Students Read

Summarizing

Summarizing the information presented in the text will help students to focus on main ideas and remember what they read. Have students read the paragraphs describing the types of plantlike protists and summarize them by restating the main ideas in their own words.

L2

Skills Focus

Predicting

Materials

euglena culture, plastic petri dish, aluminum foil, compound microscope

Time

20 minutes

Tips

Tell students to record their predictions and the reasons for them.

L2

Expected Outcome

Students will probably predict that the euglena will move toward the light because it needs light to make food. The result of the experiment will confirm this prediction. The covered area will no longer be green, because the euglena have moved to the uncovered area and the light.

Extend Ask students to identify the source of the green tint of the euglena culture. (Chloroplasts) learning modality: visual

474 ◆

Contractile vacuole

Nucleus

Pellicle

Flagellum

Chloroplast(used in food production)

Eyespot

PredictingPredict what will happen when you pour a culture of euglena into a petri dish, and then cover half the dish with aluminum foil. Give a reason for your prediction.

Then carry out the experi-ment with a culture of euglena in a plastic petri dish. Cover half the dish with alu-minum foil. After 10 minutes, uncover the dish. What do you observe? Was your pre-diction correct? Explain why euglena behave this way.

FIGURE 26Euglena The euglena is a common euglenoid that lives in fresh water. In sunlight, many euglenas can make their own food. Without sunlight, they obtain food from their environment. Interpreting Diagrams What structures help a euglena find and move toward light?

Euglenoids Euglenoids (yoo GLEE noydz) are green, unicel-lular algae that are found mostly in fresh water. Unlike otheralgae, euglenoids have one animal-like characteristic—theycan be heterotrophs under certain conditions. When sunlightis available, most euglenoids are autotrophs that produce theirown food. However, when sunlight is not available, euglenoidswill act like heterotrophs by obtaining food from their envi-ronment. Some euglenoids live entirely as heterotrophs.

In Figure 26, you see a euglena, which is a common eugle-noid. Notice the long, whiplike flagellum that helps the organ-ism move. Locate the eyespot near the flagellum. Although theeyespot is not really an eye, it contains pigments. These pig-ments are sensitive to light and help the euglena recognize thedirection of a light source. You can imagine how importantthis response is to an organism that needs light to make food.

Red Algae Almost all red algae are multicellular seaweeds.Divers have found red algae growing more than 260 metersbelow the ocean’s surface. Their red pigments are especiallygood at absorbing the small amount of light that is able toreach deep ocean waters.

People use red algae in a variety of ways. Carrageenan(ka ruh JEE nun) and agar, substances extracted from red algae,are used in products such as ice cream and hair conditioner.For people in many Asian cultures, red algae is a nutrient-richfood that is eaten fresh, dried, or toasted.


475


Use Visuals: Figure 8

Euglena

Focus

Emphasize that a unicellular organism can have functional structures.

Teach

Ask:

How many cells does a euglena have?

(One)

Point out that structures such as flagella, the eyespot, and the chloroplast are all part of the same cell. Some students may be confused that a unicellular organism has so many parts. Explain that a cell is the smallest structure capable of performing all the functions required for life.

Apply

Ask:

Is the cell shown in the figure specialized to do certain tasks?

(No, it performs all the functions necessary to maintain the euglena’s life.)


Address Misconceptions

Red Algae Are Not Always Red

Focus

Explain that algae contain other pigments in addition to the dominant pigment. The combination of pigments creates a great variety of colors.

Teach

Students may think that all green algae look green, all red algae look red, and all brown algae look brown. Inform them that although these algae contain the pigment in their names, they also contain other pigments, sometimes in such concentrations that, for example, a red alga may actually look pink or purple.

Apply

Remind students that plant leaves also contain pigments. Ask:

What is the function of the pigments in algae and in plant leaves?

(They absorb light needed for the algae and plants to make food.)


L1

Special Needs

Identifying Protists

Display in stations around the room pictures of various protists, such as slime molds, paramecia, euglenoids, diatoms, and algae. Have small groups list on index cards the characteristics they observe in the pictures. Next display three headings on the board: animal-like protists, plantlike protists, and

L1

funguslike protists. Have students attach under the appropriate headings the index cards containing the protist traits observed in the pictures. Discuss any overlap of traits among the protist groups, and ask students if it is possible to create an operational definition of a protist.


Monitor Progress L2

Writing

Ask students to describe the characteristics of diatoms, euglenoids, or red algae. Students can save their descriptions in their portfolios.

Answers

Figure 8

The eyespot helps the euglena find light, and the flagellum helps the euglena move toward light.

Figure 10

The holdfasts resemble roots and the blades resemble leaves.

Brown, green, yellow, and orange.

Chapter 11 ◆ 475

Blade

BladderStalk

Holdfast

FIGURE 27Green Algae Green algae range in size from unicellular organisms to multicellular seaweeds. This multicellular sea lettuce, Ulva, lives in oceans.

FIGURE 28Brown AlgaeGiant kelps are brown algae that have many plantlike structures.Interpreting Diagrams What plant structures do the kelp’s holdfasts and blades resemble?

Green Algae Green algae, which contain green pigments, arequite diverse. Most green algae are unicellular. Some, however,form colonies, and a few are multicellular. Most green algae livein either fresh water or salt water. The few that live on land arefound on rocks, in the crevices of tree bark, or in moist soils.

Green algae are actually very closely related to plants that liveon land. Green algae and plants contain the same type of greenpigment and share other important similarities. In fact, somescientists think that green algae belong in the plant kingdom.

Brown Algae Many of the organisms that are commonlycalled seaweeds are brown algae. In addition to their brown pig-ment, brown algae also contain green, yellow, and orange pig-ments. As you can see in Figure 28, a typical brown alga hasmany plantlike structures. Holdfasts anchor the alga to rocks.Stalks support the blades, which are the leaflike structures of thealga. Many brown algae also have gas-filled sacs called bladdersthat allow the algae to float upright in the water.

Brown algae flourish in cool, rocky waters. Brown algaecalled rockweed live along the Atlantic coast of North America.Giant kelps, which can grow as long as 100 meters, live in somePacific coastal waters. The giant kelps form large underwater“forests” where many organisms, including sea otters and aba-lone, live.

Some people eat brown algae. In addition, substancescalled algins are extracted from brown algae and used as thick-eners in puddings and other foods.

What color pigments can brown algae contain?

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Funguslike Protists

Teach Key ConceptsExploring Funguslike ProtistsFocus Review with students the characteristics of fungi: heterotrophs, have cell walls, use spores to reproduce.

Teach With students, prepare a chart or start a Venn diagram to show basic characteristics of plants, animals, and fungi. Illustrate your answers: How are funguslike protists like animals? (They are heterotrophs.) How are they like plants? (Their cells have cell walls; they use spores to reproduce.) Which of these traits do fungi also exhibit? (They have cell walls, are heterotrophs, and, reproduce with spores)

Apply Ask: How have funguslike protists caused human deaths? (Water molds destroyed the Irish potato crops in 1845 and 1846, triggering starvation.) learning modality: visual

Observing Slime Mold

Materials compound microscope, slime mold culture, plastic petri dish with cover, oatmeal

Time 15 minutes for setup, 10 minutes for observation after 24 hours

Focus Tell students that individual slime mold cells can join together and respond to stimuli as a giant mass.

Teach Pair students; give each pair a covered petri dish containing slime mold culture to observe under the microscope. Ask students to predict how slime molds will react when oatmeal is placed in the dish. Students can test predictions by uncovering the dish, putting a few flakes about 1 mm from a branch of the slime mold, and putting the cover back on. After 24 hours in a cool, dark place, the slime mold should increase in size, spread across, and engulf the oatmeal.

Apply Ask: What did you observe that suggests the slime mold is alive? (It moved toward the oatmeal and engulfed it.) learning modality: visual

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FIGURE 29Slime Molds The chocolate tube slime mold first forms a tapioca-like mass (top). When conditions become harsh, the mass grows spore-producing stalks (right). The stalks, or “chocolate tubes,” are covered with millions of brown spores.

Funguslike ProtistsThe third group of protists are the funguslike protists. Fungiinclude organisms such as mushrooms and yeast. Until youlearn more about fungi in Section 5, you can think of fungi asthe “sort of like” organisms. Fungi are “sort of like” animalsbecause they are heterotrophs. They are “sort of like” plantsbecause their cells have cell walls. In addition, most fungi usespores to reproduce. A spore is a tiny cell that is able to growinto a new organism.

Like fungi, funguslike protists are heterotrophs, have cellwalls, and use spores to reproduce. All funguslike protistsare able to move at some point in their lives. The three typesof funguslike protists are slime molds, water molds, and downymildews.

Slime Molds Slime molds are often brilliantly colored. Theylive on forest floors and other moist, shady places. They oozealong the surfaces of decaying materials, feeding on bacteriaand other microorganisms. Some slime molds are so small thatyou need a microscope to see them. Others may cover an areaof several meters!

Slime molds begin their life cycle as tiny, individualamoeba-like cells. The cells use pseudopods to feed and creeparound. Later, the cells grow bigger or join together to form agiant, jellylike mass. In some species, the giant mass is multi-cellular and forms when food is scarce. In others, the giantmass is actually a giant cell with many nuclei.

The mass oozes along as a single unit. When environ-mental conditions become harsh, spore-producing struc-tures grow out of the mass and release spores. Eventuallythe spores develop into a new generation of slime molds.


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AnswersIn water or moist places

Assess

Reviewing Key Concepts1. a. Protozoans with pseudopods, protozoans with cilia, protozoans with flagella, protozoans that are parasites b. Similar to animals: they are heterotrophs that can move from place to place; different: they are unicellular. c. As a protozoan with pseudopods.2. a. They are autotrophs. b. Their pigments absorb the sunlight, which they need to make food. c. Possible answer: Although euglena have animal-like and plantlike characteristics, they should probably be classified as plantlike protists because they have the unique ability to make thier own food.3. a. Slime molds, water molds, downy mildews b. They are heterotrophs, have cell walls, and use spores to reproduce.

ReteachDiscuss the characteristics shared by all protists, then use a “quiz bowl” format to classify protists by animal-like, plantlike, and funguslike traits.

Performance AssessmentWriting Ask students to imagine they are a paramecium. Have them write a short story of their encounters with other microscopic life forms such as amoebas, euglenoids, slime molds, and other protists. Encourage students to describe how these organisms behave and how to identify them.

Students can save their stories in their portfolios.

Teaching Resources

• Section Summary: Protists• Review and Reinforce: Protists• Enrich: Protists

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Algae Scavenger Hunt Encourage students to explain to family members that algae can be found in many products such as ice cream, hair conditioners, toothpaste, and scouring products. Students may wish to see who can find the most products containing algae.

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FIGURE 30Water Molds and Downy Mildews Many water molds are decomposers of dead aquatic organisms. Others are parasites of fish and other animals. Downy mildews are parasites of many food crops.

Water mold on fish

Downy mildew on grape leaf

Algae Scavenger Hunt Look around your house with a family member to find products that contain substances made from algae. Look at both food and nonfood items. Before you begin, tell your family member that substances such as diatomaceous earth, algin, and carrageenan are products that come from algae. Make a list of the products and the algae-based ingredient they contain. Share your list with the class.

Water Molds and Downy Mildews Most water moldsand downy mildews live in water or moist places. These organ-isms often grow as tiny threads that look like fuzz. Figure 30shows a fish attacked by a water mold and a leaf covered bydowny mildew.

Water molds and downy mildews attack many food crops,such as potatoes, corn, and grapes. A water mold impacted his-tory when it destroyed the Irish potato crops in 1845 and 1846.The loss of these crops led to a famine. More than one millionpeople in Ireland died, and many others moved to the UnitedStates and other countries.

In what environments are water molds found?

Section 1 Assessment

Target Reading Skill Outlining Use your outline about protists to help you answer the questions below.

Reviewing Key Concepts1. a. Listing List the four types of animal-like protists. How

does each type move or live?b. Comparing and Contrasting How are these four types

of protists similar to animals? How are they different?c. Classifying You observe an animal-like protist under

the microscope. It has no hairlike or whiplike structures. It moves by forming temporary bulges of cytoplasm. How would you classify this protist?

2. a. Reviewing In what way are diatoms, dinoflagellates, and other plantlike protists similar to plants?

b. Making Generalizations Why is sunlight important to plantlike protists?

c. Making Judgments Would you classify euglena as an animal-like protist or as a plantlike protist? Explain.

3. a. Listing What are the three types of funguslike protists?b. Describing In what ways are funguslike protists similar

to fungi?

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